Question

情况：你有一个嵌套循环，你需要突破它。

让我们看看这个经典的例子（经典，因为它来自Goto Considered Harmful Considered Harmful）：给定一个二维NxN方形整数矩阵X，找到没有零的第一行。

我将通过几种不同语言解决这个问题的方法。我想我应该从的编写方式开始，但不是。

//using "chained breaks"
for(int i=0;i<N;i++){
    for(int j=0;j<N;j++){
        if( X[i][j] == 0 ){
            //this row isn't non-zero, so go to the next row
            break continue;
                //break out of the inner loop and continue the outer loop
        }
    }
    //if we get to here, we know this row doesn't have zeroes
    return i;
}
return -1; //failure; exact val doesn't matter for this question

C及其主要忠实的衍生品：

//goto
for(int i=0;i<N;i++){
    for(int j=0;j<N;j++){
        if( X[i][j] == 0 ){
            //this row isn't non-zero, so go to the next row
            goto next; //skip past the return
        }
    }
    //if we get to here, we know this row doesn't have zeroes
    return i;
    label next;
}
return -1; //failure; exact val doesn't matter for this question

爪哇：

//labeled loops and labeled break/continue
outer: for(int i=0;i<N;i++){
    for(int j=0;j<N;j++){
        if( X[i][j] == 0 ){
            //this row isn't non-zero, so go to the next row
            continue outer; //go to the next row
        }
    }
    //if we get to here, we know this row doesn't have zeroes
    return i;
}
return -1; //failure; exact val doesn't matter for this question

PHP：

//this PHP may be wrong, it's been a while
for($i=0;$i<$N;$i++){
    for($j=0;$j<$N;$j++){
        if( $X[$i][$j] == 0 ){
            //this row isn't non-zero, so go to the next row
            continue 2;
                //continue the outer loop
        }
    }
    //if we get to here, we know this row doesn't have zeroes
    return $i;
}
return -1; //failure; exact val doesn't matter for this question

使用旗帜：

//using a flag
for(int i=0;i<N;i++){
    bool foundzero = false;
    for(int j=0;j<N;j++){
        if( X[i][j] == 0 ){
            //this row isn't non-zero, so go to the next row
            foundzero = true;
            break; //go to the next row
        }
    }
    //if we get to here, we know this row doesn't have zeroes
    if(!foundzero)
        return i;
}
return -1; //failure; exact val doesn't matter for this question

将内循环导出到函数：

//using a function call
for(int i=0;i<N;i++){
    if(haszero(X[i],N))
        return i;
}
return -1; //failure; exact val doesn't matter for this question

//and the haszero function
bool haszero(int arr[], int N){
    for(int i=0;i<N;i++){
        if( arr[i] == 0 ){
            return false;
        }
    }
    return true;
}

现在，所有这些工作，但有些功能调用开销（如果语言想要允许深度循环则很糟糕），标志（对某些人来说令人反感或不直观），goto（比你可能需要的更强大）），或奇怪的语法（Java的愚蠢）。

那么为什么语言没有break break，break continue，break break continue等？（continue break毫无意义，因为它意味着进入下一次迭代然后离开它。将这类内容添加到语言中是否存在问题？

为什么不“突破”呢？

0 个答案: